tictoc-6
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Requirements and viewpoints for backhaul synchronization
draft-zhou-tictoc-ran-sync-req-00.txt
Angela Zhou, Xiaodong DuanChina Mobile
Synchronization in 2G/GSM• Current 2G/GSM Networks
• Sync Requirements in current 2G/GSM Networks
– SDH transport network need frequency sync: +/- 50ppm
– Base stations need frequency sync: +/- 0.05ppm
– Reference clock is distributed via an explicit transport at the physical layer: PDH/SDH
• Future 2G/GSM Networks
• Sync Requirements in future 2G/GSM Networks
– Packet switching network do not need strict synchronization
– Base stations need frequency sync: +/- 0.05ppm– For base stations, Reference clock is distributed via
PSN, need physical synchronization support (e.g. Sync Ethernet) or packet-based synchronization (e.g. 1588).
Note: Previous SDH transport network maybe still exist for traditional base stations, sync requirement is the same as before.
BTS BSC
Ref. clockMS
SDH
E1 E1
BTSBSC
Ref. clock
MS
IP BSC
MS
PSN
IP BTS
Circuit Emulation
E1 E1
FE GE
Synchronization in 3G/TD-SCDMA• Current trail 3G/TD-SCDMA
Networks
• Sync Requirement in current 3G/TD-SCDMA Networks
– SDH transport network need frequency sync: +/- 50ppm
– For transport network, Reference clock is distributed via an explicit transport at the physical layer: PDH/SDH
– Base stations need frequency sync: +/- 0.05ppm, and phase sync: +/- 3us
– For base stations, reference clock is distributed via GPS
• Future 3G/TD-SCDMA Networks
• Sync Requirement in future 3G/TD-SCDMA Networks
– Packet switching network do not need strict synchronization
– Base stations need frequency sync: +/- 0.05ppm, and phase sync: +/- 3us
– For base stations, reference clock is distributed via PSN, need physical synchronization support (e.g. Sync Ethernet) for frequency sync or packet-based synchronization (e.g. 1588) for time/phase sync.
RNC
NodeB
NodeB SDH
ATM
ATMRNC
NodeB
NodeB PSN
FE
GE
Ref. clock
Synchronization in 4G/TDD-LTE/FDD-LTE
• Possible synchronization requirements in LTE– Synchronization requirements in ALL-IP network– Synchronization requirements in distributing Base Station
(mesh topology among base stations)– Synchronization requirements in distributing BBU & RRU– Synchronization requirements in radio interfaces
Note: synchronization requirement in LTE is under discussion.
AGW
eNB
eNB
PSN
Ref. clock
eNB
eNB
eNB
eNB
eNB
Synchronization in different partsBase station Base
station controller
Base station
UE
UE
RadioInterface
SYNC
Ref. Clock
Network SYNCNode SYNC
• Requirements schematic diagram
• Synchronization requirements in different positions
Layer Sub Items Frequency Accuracy Phase Accuracy
Network Sync E1 50ppm -
STM-N 4.6ppm -
PTN Not so strict -
Node Sync Controller-Base station
50ppb(If base station pick up time from base station controller)
3us(if base station pick up time from base station controller)
Inter-Base station 50ppb(If base station pick up time from other base station)
3us(If base station pick up time from other base station)
Radio interface GSM 50ppb -
WCDMA 50ppb -
TD-SCDMA 50ppb 3us
TDD LTE 50ppb TBD
FDD LTE 50ppb -
Mobile backhaul• Mobile backhaul could be based on
– Carrier Ethernet (e.g. 802.1ad, PBB-TE)– IP/MPLS (e.g. PW, VPLS, L3VPN ,IP routing)– T-MPLS– Others
• Each transport technique can fit certain scenario respectively, and they could be used in different network layers (access/aggregation/core).
Mobile backhaul• Mobile backhaul network
Base station
IP/MPLScore
Base stationcontrollerPBTBase
station
802.1ad
Base station
DLS
PON
Base stationcontroller
Base station
IP/MPLScore
Base stationcontrollerTMPLSBase
station
TMPLS
Base stationcontroller
TMPLS
Base stationcontrollerBase
station
IP/MPLScore
Base stationcontrollerBase
stationMPLS AGGVLL/VPLS
MPLS Access
802.1ad
CoreAggrAccess
SON & Self-backhauling
AGW 1AGW 2
New BSJoin
Ref. Clock
• Self Organization Network– Some BSs are configured
only by it’s mother BS for both sync and radio resource
• Self-backhauling– Using in-band connection
between BSs for backhaul
Concerns & Summary• The requirements for RAN is clear and urgent
– Radio Access Network is on the early stage of moving to IP transport– Using GPS will affect the flexible deployment of BS, we really need a new
synchronization technology to substitute GPS, epically though a simple Ethernet port
– How to distribute synchronization through packet based network? Can 1588 meet our requirements? Telecom profiles of 1588 should be standardized:
• network scale/ network load/ local clock accuracy• Security
– The synchronization methods in next generation mobile network (LTE) and MESH/SON network should be paid more attention.
• At the same time, it is complex and more technologies in backhaul– How to extend IEEE1588 or other synchronization technology so that it can be
used smoothly in PBN and complex backhaul.– Features needed for Backhaul nodes to support 1588 for high accuracy– Different layers shall collaborate to meet the sync requirements form end to end,
so what kind of mechanisms/protocols are need between different layer and technologies in backhaul?
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